Vehicle control apparatus

ABSTRACT

A vehicle control apparatus is provided, which includes a sensor; and a processing device that calculates a SOC, determines whether the calculation value of the SOC is greater than a predetermined threshold, and permits execution of control that involves a discharge of a battery if the SOC is greater than the predetermined threshold. When the processing device detects a decrease in accuracy of the SOC, the processing device determines whether the calculation value of the SOC at a time of detection of the decrease is greater than a predetermined value, and if yes, corrects the SOC, etc., to continue the determination with the predetermined threshold, such that the execution of the control is permitted more difficulty, within a range in which the execution of the control can be permitted, with respect to a state before the detection.

FIELD

The disclosure is related to a vehicle control apparatus.

BACKGROUND

Japanese Laid-open Patent Publication No. 05-087896 (Patent Document 1)discloses a battery rest quantity detection/correction method thatincludes a consumed electric current calculation part for accumulatingthe consumed electric current supplied from a battery and a battery restquantity correction part for correcting the battery rest quantitycalculation value at each prescribed voltage which is obtained from thevalue accumulated by the consumed electric current calculation part,based on the actual battery rest quantity at each prescribed voltage ofthe battery.

It is useful to suppress control that involves a discharge of a battery(fuel economy control such as charge control, idling stop control, forexample) in terms of a battery reservation, if a SOC (State Of Charge)of the battery becomes less than a predetermined level.

The SOC of the battery is calculated from a current accumulation value,etc., based on sensor information, and thus there may be a case whereaccuracy of a calculation value (estimation value) of the SOC isdecreased. If an execution of the control that involves the discharge ofthe battery is permitted based on the calculation value with thedecreased accuracy, there may be a risk that an actual SOC of thebattery decreases below a lower limit value, leading to an undesiredcase in terms of the battery reservation. For this reason, there may besuch a solution in which, if the calculation accuracy of the SOC of thebattery is decreased, the execution of the control that involves thedischarge of the battery may be prevented until a correction valuesuited for a decreased accuracy state is obtained. However, according tosuch a solution, there may be a risk that a chance to execute thecontrol that involves the discharge of the battery may be limited morethan necessary.

Therefore, the disclosure is to provide a vehicle control apparatus thatis capable of appropriately reducing a limitation on an execution ofcontrol that involves a discharge of a battery when a decrease inaccuracy of a calculation value of a SOC is detected.

SUMMARY

According to one aspect of the disclosure, a vehicle control apparatusis provided, which includes:

-   -   a sensor that obtains information related to a SOC (State Of        Charge) of a battery; and    -   a processing device that calculates the SOC based on the        information from the sensor; determines whether the calculation        value of the SOC is greater than a predetermined threshold; and        permits an execution of control that involves a discharge of the        battery if the calculation value of the SOC is greater than the        predetermined threshold, wherein    -   when the processing device detects a decrease in accuracy of the        calculation value of the SOC, the processing device determines        whether the calculation value of the SOC at a time of detection        of the decrease is greater than a predetermined value that is        greater than the predetermined threshold, and if the calculation        value of the SOC at a time of detection of the decrease is        greater than the predetermined value, the processing device        corrects at least one of the calculation value of the SOC and        the predetermined threshold to continue the determination with        the predetermined threshold, wherein at least one of the        calculation value of the SOC and the predetermined threshold is        corrected such that the execution of the control is permitted        more difficulty, within a range in which the execution of the        control can be permitted, with respect to a state before the        detection of the decrease.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram illustrating a configuration of a power supplysystem of a vehicle according an embodiment.

FIG. 2 is a diagram illustrating a system configuration of a controlsystem of a vehicle according an embodiment.

FIG. 3 is a diagram illustrating an example of a functionalconfiguration of a battery capacity calculation part 14.

FIG. 4 is a diagram for explaining a first correction value Δ1 for highaccuracy state and a second correction value Δ2 for low accuracy state.

FIG. 5 is an example of a flowchart of a process executed by a chargecontrol ECU 10.

FIG. 6 is a diagram illustrating an example of a change in time seriesof a control SOC based on an accuracy reservation margin M and a controlSOC for high accuracy state.

FIG. 7 is a diagram illustrating an example of a change in time seriesof the control SOC in a high accuracy state and a low accuracy state.

FIG. 8 is a timing chart illustrating an example of a way of calculatingthe second correction value Δ2 for the low accuracy state based onbehavior of a charge current I of a battery 60.

DESCRIPTION OF EMBODIMENTS

In the following, embodiments will be described with reference to theaccompanying drawings.

FIG. 1 is a diagram for illustrating a configuration of a power supplysystem of a vehicle according an embodiment. The embodiment is suitedfor the vehicle that has only an engine installed as a power source(i.e., other than hybrid vehicles and electric vehicles), as illustratedin FIG. 1. In a configuration illustrated in FIG. 1, an alternator 40 ismechanically connected to an engine 42. The alternator 40 is a generatorthat generates electricity based on power of the engine 42. The electricpower generated by the alternator 40 is utilized for charging a battery60 and driving vehicle electric loads 50. It is noted that a currentsensor 62 is provided for the battery 60. The current sensor 62 detectsa battery current (i.e., a charge current to the battery 60 and adischarge current from the battery 60). Typically, the battery 60 is alead acid battery; however, other types of batteries (or capacitors) maybe used. A voltage sensor 64 is provided for the battery 60. It is notedthat the voltage sensor 64 and the current sensor 62 may be formed by asingle sensor unit 65 in which the voltage sensor 64 and the currentsensor 62 are incorporated together with a processor (a microcomputer,for example). The sensor unit 65 may be a sensor that is referred to asan intelligent battery sensor or the like, for example. Further, thecurrent sensor 62 may be a shunt resistance, for example, and thevoltage may be calculated based on a product of the current valuedetected by the current sensor 62 and a resistance value of the shuntresistance. In this case, the current sensor 62 also serves as thevoltage sensor 64. The vehicle electric loads 50 are arbitrary, andinclude a starter, an air conditioner, a wiper, etc. In such aconfiguration, by controlling a voltage generated by the alternator 40,a SOC (State Of Charge) of the battery 60 can be controlled.

FIG. 2 is a diagram illustrating a system configuration of a controlsystem of a vehicle according an embodiment.

A control system 1 includes a charge control ECU (Electronic ControlUnit) 10 and an idling stop control ECU 30. It is noted that connectionways between elements in FIG. 2 are arbitrary. For example, theconnection ways may include a connection via a bus such as a CAN(controller area network), etc., an indirect connection via another ECU,etc., a direct connection, and a connection that enables wirelesscommunication. It is noted that sections of the functions of the ECUsare arbitrary, and a part or all of the functions of a particular ECUmay be implemented by another ECU (which may include an ECU notillustrated). For example, a part or all of the functions of the chargecontrol ECU 10 may be implemented by the idling stop control ECU 30, orreversely a part or all of the functions of the idling stop control ECU30 may be implemented by the charge control ECU 10. Further, if thesensor unit 65 in which a microcomputer is incorporated is used, a partof a function of the charge control ECU 10 may be implemented by themicrocomputer in the sensor unit 65. For example, a part of or all of abattery capacity calculation part 14 may be implemented by themicrocomputer in the sensor unit 65.

The charge control ECU 10 may be implemented by an engine ECU forcontrolling the engine, for example. The charge control ECU 10 includesa battery state determination part 12, a battery capacity calculationpart 14, a charge/discharge amount calculation part 15, an electricpower generation voltage instruction part 16 and a fuel economyprevention part 18, as illustrated in FIG. 2. It is noted that theseparts merely represent functions implemented by software resources, andthe sections are also arbitrary. Thus, a part of or all of a programthat implements the battery state determination part 12 and/or thecharge/discharge amount calculation part 15, for example, may beincorporated into a program that implements the battery capacitycalculation part 14.

The battery state determination part 12 determines a degradation degreeof the battery 60. Ways of determining the degradation degree of thebattery 60 are various, and an arbitrary way may be used. For example,the degradation degree of the battery 60 is related to an internalresistance of the battery 60, and thus the degradation degree of thebattery 60 may be calculated according to the internal resistance of thebattery 60.

The battery capacity calculation part 14 calculates the current SOC ofthe battery 60. The battery capacity calculation part 14 outputs acontrol SOC based on the calculated SOC of the battery 60. Details ofthe battery capacity calculation part 14 are described hereinafter.

The charge/discharge amount calculation part 15 calculates a cumulativecharge/discharge electricity amount based on the detection values of thecurrent sensor 62. The cumulative charge/discharge electricity amountmay be a time-integrated value of the charge current and the dischargecurrent such that the charge current and the discharge current areintegrated with absolute values thereof. In the following, as anexample, it is assumed that the charge/discharge amount calculation part15 calculates the cumulative charge/discharge electricity amount fromthe time of the ignition switch ON event. In other words, the cumulativecharge/discharge electricity amount is reset to an initial value 0 whenthe ignition switch is turned off.

The electric power generation voltage instruction part 16 performscharge control under a situation where the charge control is notprevented by fuel economy prevention part 18 as described hereinafter.Specifically, the electric power generation voltage instruction part 16determines a power generation voltage (target value) of the alternator40 based on a vehicle traveling state, and the control SOC calculated inthe battery capacity calculation part 14. The vehicle travel stateincludes a vehicle stop state, an accelerated state, a constant vehiclespeed state, a decelerated state, etc., for example. A way ofdetermining the electric power generation voltage of the alternatoraccording to the vehicle travel state is arbitrary. For example, in theconstant vehicle speed state in which the vehicle speed is substantiallyconstant, the electric power generation voltage instruction part 16instructs the electric power generation voltage of the alternator 40such that the control SOC is kept at a constant value a (smaller than100%). Further, in the accelerated state, the electric power generationvoltage instruction part 16 stops the electric power generation of thealternator 40 to increase an accelerating ability. In the deceleratedstate, the electric power generation voltage instruction part 16performs an electric power regenerating operation of the alternator 40.It is noted that, when an idling stop control is performed in thevehicle stop state, the alternator 40 is stopped during a period inwhich the idling stop control is being performed.

The electric power generation voltage instruction part 16 instructs apredetermined constant value as the electric power generation voltage ofthe alternator 40, regardless of the vehicle travel state, etc., in asituation where the charge control is prevented by the fuel economyprevention part 18 as described hereinafter. The predetermined constantvalue may be set such that the battery 60 is brought to its fullycharged state and kept in the fully charged state, for example.Alternatively, the electric power generation voltage instruction part 16may instruct the electric power generation voltage of the alternator 40such that the control SOC calculated by the battery capacity calculationpart 14 become 100%.

The fuel economy prevention part 18 performs a process (referred to as“a fuel economy control execution propriety determination process”hereinafter) for determining whether an execution of the fuel economycontrol can be performed. Specifically, the fuel economy prevention part18 determines whether the control SOC becomes less than or equal to apredetermined threshold (referred to as “a control permission SOC”,hereinafter). The fuel economy prevention part 18 outputs a preventioninstruction for preventing the execution of the fuel economy control ifthe control SOC becomes less than or equal to the control permissionSOC. The fuel economy control is performed for the purpose of increasingthe fuel economy. The fuel economy control includes a charge control andan idling stop (Stop and Start) control, in this example. Thus, in thisexample, the fuel economy prevention part 18 prevents the charge controland the idling stop control by the idling stop control ECU 30, if thecontrol SOC becomes less than or equal to the control permission SOC.

Further, the fuel economy prevention part 18 outputs the preventioninstruction for preventing the fuel economy control during a refreshcharging. In other words, the fuel economy prevention part 18 preventsthe charge control and the idling stop control by the idling stopcontrol ECU 30 during the refresh charging. A way of performing therefresh charging is arbitrary. Typically, the refresh charging includescharging the battery 60 to reach a charge late state in which the chargecurrent of the battery 60 becomes less than a predetermined value or anovercharged state. A start condition of the refresh charging isarbitrary. In the present embodiment, the start condition of the refreshcharging is met if it becomes necessary to perform a calculation processfor calculating a second correction value Δ2 for low accuracy state(described hereinafter). Further, the refresh charging may be performedif the degradation degree of the battery 60 determined by the batterystate determination part 12 exceeds a predetermined threshold, etc.

The idling stop control ECU 30 performs the idling stop control. Theidling stop control is also referred to as “S & S (Stop & Start)”. Thedetails of the idling stop control are arbitrary. Typically, the idlingstop control stops the engine 42 when a predetermined idling stop startcondition is met in the vehicle stop state or the decelerated state in alow-speed range, and then restarts the engine 42 when a predeterminedidling stop end condition is met. The predetermined idling stop startcondition includes a condition where a prevention instruction is notoutput from the fuel economy prevention part 18. In other words, if theprevention instruction is generated by the fuel economy prevention part18 (i.e., the fuel economy control is prevented by the fuel economyprevention part 18), the idling stop control is also prevented and thusis not performed.

FIG. 3 is a diagram illustrating an example of a functionalconfiguration of a battery capacity calculation part 14.

The battery capacity calculation part 14 includes a SOC calculation part141, a calculation accuracy determination part 142, a correction valuecalculation part 143, and a control SOC calculation part 144.

The SOC calculation part 141 calculates the current SOC of the battery60 based on the detection values of the current sensor 62, etc. Aconcrete way of calculating the SOC of the battery 60 may be arbitrary.For example, the current SOC of the battery 60 can be calculated basedon the SOC of the battery 60 in an ignition switch OFF state and adifference between a charge amount of electricity and a discharge amountof electricity after the time of the ignition switch ON event. The SOCof the battery 60 in the ignition switch OFF state may be calculatedbased on an OCV (Open Circuit Voltage) that is obtained from the voltagesensor 64 in the ignition switch OFF state or immediately after theignition switch ON event. Further, the SOC of the battery 60 may becorrected based on a temperature of the battery 60, etc. In thefollowing, the calculation value of the SOC calculated by the SOCcalculation part 141 is also referred to as “a pre-correction SOC”,hereinafter.

The calculation accuracy determination part 142 detects a decrease inthe accuracy of the pre-correction SOC calculated by the SOC calculationpart 141. It is noted that such a decrease of the accuracy results froma fact that an error is inevitably included in a detection current valueof the current sensor 62 due to hardware related factors of the currentsensor 62. A way of detecting the decrease in the accuracy of thepre-correction SOC calculated by the SOC calculation part 141 isarbitrary. For example, the calculation accuracy determination part 142may detect the decrease in the accuracy of the pre-correction SOC basedon the cumulative charge/discharge electricity amount. For example, thecalculation accuracy determination part 142 may detect the decrease inthe accuracy of the pre-correction SOC if the cumulativecharge/discharge electricity amount exceeds a predetermined thresholdTh2. This is because the effect due to a cumulative error cannot beneglected as the cumulative charge/discharge electricity amount becomesgreater. Alternatively, from the same viewpoint, the calculationaccuracy determination part 142 may detect the decrease in the accuracyof the pre-correction SOC based on lapsed time, travel distance, etc.,from the time of the ignition ON event. Further, the calculationaccuracy determination part 142 may consider a soak time. This isbecause the shorter the soak time becomes, the greater the decrease inthe accuracy of the pre-correction SOC calculated based on the OCV atthe time of the ignition ON event becomes. For example, the calculationaccuracy determination part 142 may set the predetermined value Th2 suchthat the shorter the soak time becomes, the smaller the predeterminedvalue Th2 becomes.

The calculation accuracy determination part 142 detects the decrease inthe accuracy of the pre-correction SOC calculated by the SOC calculationpart 141 in any number of steps. In the following, as an example, thecalculation accuracy determination part 142 determines two states “ahigh accuracy state” and “a low accuracy state” (i.e., in two steps)with respect to the accuracy of the pre-correction SOC calculated by theSOC calculation part 141. For example, the calculation accuracydetermination part 142 sets the high accuracy state at the time of theignition switch ON event, and sets the low accuracy state if thecumulative charge/discharge electricity amount exceeds the predeterminedvalue.

The correction value calculation part 143 calculates a correctionvalue(s) for the pre-correction SOC calculated by the SOC calculationpart 141. The correction values may include the first correction valueΔ1 for high accuracy state and the second correction value Δ2 for lowaccuracy state. A way of calculating a first correction value Δ1 forhigh accuracy state is arbitrary. For example, the first correctionvalue Δ1 for high accuracy state may be a constant value. The constantvalue may be adapted by experiments, etc. The correction valuecalculation part 143 may calculate the second correction value Δ2 forlow accuracy state based on behavior of the charge current during therefresh charging. For example, the second correction value Δ2 for lowaccuracy state is a value according to a difference D between a firstcorrection value α1 of the SOC calculated based on the behavior of thecharge current in the charge late state during the refresh charging, anda second correction value α2 of the SOC calculated based on the voltageof the battery 60 at the same timing as the first correction value α1.In other words, the second correction value α2 corresponds to the SOCcalculated by using the voltage of the battery 60 in the charge latestate based on a relationship between the voltage of the battery 60 andthe SOC. The second correction value α2 may correspond to the differenceD or may be a value obtained by multiplying the difference D by apredetermined proportionality factor, for example. The first correctionvalue α1 may be calculated based on the behavior (change manner in timeseries) of the charge current measured by the current sensor 62according to a known charge characteristic of the battery 60, forexample. The charge characteristic is related a relationship between thecharge current and the SOC. The correction value calculation part 143utilizes data representing the charge characteristic of the battery 60measured in advance, for example.

The control SOC calculation part 144 calculates the control SOC based onthe pre-correction SOC calculated by the SOC calculation part 141 andthe correction value calculated by the correction value calculation part143. At that time, the control SOC calculation part 144 changes the wayof calculating the control SOC according to the accuracy determined bythe calculation accuracy determination part 142. Specifically, in thehigh accuracy state, the control SOC calculation part 144 calculates thecontrol SOC by subtracting the first correction value Δ1 for highaccuracy state from the pre-correction SOC calculated by the SOCcalculation part 141. In the low accuracy state, the control SOCcalculation part 144 calculates the control SOC by subtracting thesecond correction value Δ2 for low accuracy state from thepre-correction SOC calculated by the SOC calculation part 141. However,even in the low accuracy state, as described hereinafter, if thepre-correction SOC calculated by the SOC calculation part 141 at thetime of setting the low accuracy state is greater than a predeterminedthreshold Th1, the control SOC calculation part 144 calculates thecontrol SOC by subtracting the first correction value Δ1 for highaccuracy state from the pre-correction SOC calculated by the SOCcalculation part 141 and further subtracting a predetermined accuracyreservation margin M from the pre-correction SOC from which the firstcorrection value Δ1 for high accuracy state has been subtracted.

FIG. 4 is a diagram for explaining the first correction value Δ1 forhigh accuracy state and the second correction value Δ2 for low accuracystate, in which (A) illustrates an example of a relationship between thepre-correction SOC and an actual SOC in the high accuracy state, and (B)illustrates an example of a relationship between the pre-correction SOCand the actual SOC in the low accuracy state.

In the high accuracy state, as illustrated in FIG. 4 (A), an alienationbetween the pre-correction SOC and the actual SOC is relatively smallbecause of the high accuracy state. In the example illustrated in FIG. 4(A), the pre-correction SOC is calculated such that it is higher thanthe actual SOC. In the case of the high accuracy state, the control SOCis calculated by subtracting the first correction value Δ1 for highaccuracy state from the pre-correction SOC, which can reduce thealienation between the control SOC and the actual SOC. It is noted that,in this example, the pre-correction SOC is calculated such that it ishigher than the actual SOC; however, there may be a case where thepre-correction SOC is calculated such that it is lower than the actualSOC. In this case, the control SOC may be calculated by adding the firstcorrection value Δ1 for high accuracy state to the pre-correction SOC.

In the low accuracy state, as illustrated in FIG. 4 (B), the alienationbetween the pre-correction SOC and the actual SOC is relatively greatbecause of the low accuracy state. In the example illustrated in FIG. 4(B), the pre-correction SOC is calculated such that it is higher thanthe actual SOC. At that time, as schematically illustrated in FIG. 4(B), in the case of the low accuracy state, the control SOC iscalculated by subtracting the second correction value Δ2 for lowaccuracy state from the pre-correction SOC. The second correction valueΔ2 for low accuracy state is greater than the first correction value Δ1for high accuracy state. Thus, even in the low accuracy state, thealienation between the control SOC and the actual SOC can be reduced. Itis noted that, in this example, the pre-correction SOC is calculatedsuch that it is higher than the actual SOC; however, there may be a casewhere the pre-correction SOC is calculated such that it is lower thanthe actual SOC. In this case, the control SOC may be calculated byadding the second correction value Δ2 for low accuracy state to thepre-correction SOC.

In this way, even if the calculation accuracy of the pre-correction SOCis decreased, the alienation between the control SOC and the actual SOCcan be reduced by calculating the second correction value Δ2 for lowaccuracy state to correct the pre-correction SOC. With this arrangement,the fuel economy control execution propriety determination process basedon the control SOC can be performed continuously. With this arrangement,even if the calculation accuracy of the pre-correction SOC is decreased,the reduction in the chance to perform the fuel economy control issuppressed. However, the calculation of the second correction value Δ2for low accuracy state involves the refresh charging, as describedabove. This means that the fuel economy control is prevented during thecalculation process of the second correction value Δ2 for low accuracystate. In other words, this means that there is a case where the chanceto perform the fuel economy control is lost due to the calculation ofthe second correction value Δ2 for low accuracy state. In the following,a way of reducing the loss of the chance to perform the fuel economycontrol is described in detail.

FIG. 5 is an example of a flowchart of a process executed by the chargecontrol ECU 10. The process illustrated in FIG. 5 is initiated at thetime of the ignition switch ON event, and then may be repeated at apredetermined cycle until the ignition switch is turned off (see “YES”step S521 or step S522).

In step S500, respective operations in the high accuracy state areperformed. Specifically, the SOC calculation part 141 of the batterycapacity calculation part 14 calculates the pre-correction SOC; thecorrection value calculation part 143 calculates the first correctionvalue Δ1 for high accuracy state; and the control SOC calculation part144 of the battery capacity calculation part 14 calculates the controlSOC based on the first correction value Δ1 for high accuracy state. Inthe following, the control SOC calculated based on the first correctionvalue Δ1 for high accuracy state is also referred to as “a control SOCfor high accuracy state”, hereinafter. The fuel economy prevention part18 performs the fuel economy control execution propriety determinationprocess based on the control SOC for high accuracy state. In otherwords, the fuel economy prevention part 18 determines whether thecontrol SOC for high accuracy state becomes less than or equal to thecontrol permission SOC. The fuel economy prevention part 18 outputs aprevention instruction for preventing the execution of the fuel economycontrol if the control SOC for high accuracy state becomes less than orequal to the control permission SOC.

In step S502, the calculation accuracy determination part 142 of thebattery capacity calculation part 14 determines whether the calculationaccuracy of the pre-correction SOC is decreased. This determination waymay be as described above. If the calculation accuracy of thepre-correction SOC is decreased, the calculation accuracy determinationpart 142 sets the low accuracy state, which causes the process to go tostep S504. On the other hand, if the calculation accuracy of thepre-correction SOC is not decreased, the process returns to step S500 torepeatedly perform the respective operations in the high accuracy state.

In step S504, the correction value calculation part 143 determineswhether the second correction value Δ2 for low accuracy state hasalready been calculated. Once the second correction value Δ2 for lowaccuracy state has been calculated, it may be cleared at the time of theignition switch OFF event, or may be held over for a plurality of trips.If the second correction value Δ2 for low accuracy state has alreadybeen calculated, the process goes to step S519, otherwise the processgoes to step S506.

In step S506, the control SOC calculation part 144 determines whetherthe control SOC (control SOC for high accuracy state) at the time of thedetection of the decrease in the calculation accuracy is greater thanthe predetermined threshold Th1. The predetermined threshold Th1corresponds to a value near the lower limit value of the range of thehigh accuracy state of the battery 60. The predetermined threshold Th1is set based on design concepts. It is noted that, as a matter ofcourse, the predetermined threshold Th1 is substantially greater thanthe control permission SOC. It is noted that, instead of determiningwhether the control. SOC at the time of the detection of the decrease inthe calculation accuracy is greater than the predetermined thresholdTh1, it may be determined whether the pre-correction SOC at the time ofthe detection of the decrease in the calculation accuracy is greaterthan a predetermined threshold Th1′ as an equivalent embodiment. Also inthis case, the predetermined threshold Th1′ may be set based on the sameconcepts. Further, the control SOC at the time of the detection of thedecrease in the calculation accuracy is not necessarily the control SOCfor the accuracy state at the very time of the detection of the decreasein the calculation accuracy. The control SOC at the time of thedetection of the decrease in the calculation accuracy has such a conceptthat it includes the control SOC before or after the detection of thedecrease in the calculation accuracy as long as there is not a greatdifference with respect to the very time of the detection of thedecrease in the calculation accuracy. In step S506, if the control SOCat the time of the detection of the decrease in the calculation accuracyis greater than the predetermined threshold Th1, the process goes tostep S508, otherwise the process goes to step S514.

In step S508, the control SOC calculation part 144 calculates thecontrol SOC by subtracting the predetermined accuracy reservation marginM from the control SOC for high accuracy state. Specifically, thecontrol SOC calculation part 144 calculates the control SOC as follows.control SOC=control SOC for high accuracy state−accuracy reservationmargin M. The accuracy reservation margin M may be arbitrary. Theaccuracy reservation margin M is set in a range less than or equal to adifference between the predetermined value Th1 and the controlpermission SOC. For example, the accuracy reservation margin M may bethe previous value of the second correction value Δ2 for low accuracystate (if it is previously calculated). Alternatively, if a tolerancerange of the alienation between the pre-correction SOC in the highaccuracy state and the actual SOC (see FIG. 4 (A)) is ±X %, and atolerance range of the alienation between the pre-correction SOC in thelow accuracy state and the actual SOC (see FIG. 4 (A)) is ±Y (greaterthan X %), the accuracy reservation margin M may be equal to Y−X. It isnoted that the control SOC calculation part 144 calculates the controlSOC by subtracting a predetermined accuracy reservation margin M′ fromthe pre-correction SOC as an equivalent embodiment. In this case, thepredetermined accuracy reservation margin M′ may be set such that it isgreater than the first correction value Δ1 for high accuracy state thatotherwise is subtracted from the pre-correction SOC.

In step S510, the fuel economy prevention part 18 performs the fueleconomy control execution propriety determination process based on thecontrol SOC calculated in step S508. In other words, the fuel economyprevention part 18 determines whether the control SOC calculated in stepS508 is greater than the control permission SOC. If the control SOCcalculated in step S508 is greater than the control permission SOC, theprocess goes to step S512, otherwise the process goes to step S514.

In step S512, the fuel economy prevention part 18 permits the executionof the fuel economy control. For example, the fuel economy preventionpart 18 does not output the prevention instruction for preventing thefuel economy control. Thus, if the execution condition of the fueleconomy control is met, the fuel economy control is performed. It isnoted that, if the permission for the execution of the fuel economycontrol is implemented by not outputting the prevention instruction, theprocess of step S512 may be omitted in the software program.

In step S514, the fuel economy prevention part 18 outputs the preventioninstruction for preventing the fuel economy control. This output processof the prevention instruction is for calculating the second correctionvalue Δ2 for low accuracy state in the next process of step S516. Thisis because the calculation of the second correction value Δ2 for lowaccuracy state involves the refresh charging, as described above. Inother words, this is because, in order to calculate the secondcorrection value Δ2 for low accuracy state, the behavior of the chargecurrent during the refresh charging needs to be detected.

In step S516, the correction value calculation part 143 calculates thesecond correction value Δ2 for low accuracy state. The way ofcalculating the second correction value Δ2 for low accuracy state may beas described above.

In step S518, the fuel economy prevention part 18 cancels the preventedstate formed in step S514. It is noted that the calculation process ofthe second correction value Δ2 for low accuracy state by the correctionvalue calculation part 143 (step S516) takes time to some extent. Thus,the fuel economy prevention part 18 waits for the completion of thecalculation of the second correction value Δ2 for low accuracy state bythe correction value calculation part 143, and cancels the preventedstate after the completion of the calculation of the second correctionvalue Δ2 for low accuracy state by the correction value calculation part143.

In step S518, the control SOC calculation part 144 calculates thecontrol SOC based on the second correction value Δ2 for low accuracystate calculated in step S516. The way of calculating the control SOCfor low accuracy state based on the second correction value Δ2 for lowaccuracy state may be as described above.

In step S520, the fuel economy prevention part 18 performs the fueleconomy control execution propriety determination process based on thecontrol SOC calculated in step S519. In other words, the fuel economyprevention part 18 determines whether the control SOC calculated in stepS519 is less than or equal to the control permission SOC. If the controlSOC calculated in step S519 is less than or equal to the controlpermission SOC, the fuel economy prevention part 18 outputs theprevention instruction for preventing the execution of the fuel economycontrol. On the other hand, if the control SOC calculated in step S519is greater than the control permission SOC, the fuel economy preventionpart 18 does not output the prevention instruction (i.e., forms thepermitted state). Thus, if the execution condition of the fuel economycontrol is met, the fuel economy control is performed.

In step S521, the control SOC calculation part 144 determines whetherthe ignition switch is turned off. If the ignition switch is turned off,the process ends correspondingly (forced to end), and otherwise theprocess returns to step S508 to repeat the processes using the newlyobtained pre-correction SOC.

In step S522, the fuel economy prevention part 18 determines whether theignition switch is turned off. If the ignition switch is turned off, theprocess ends correspondingly (forced to end), and otherwise the processreturns to step S519 to repeat the processes using the newly obtainedpre-correction SOC.

According to the process illustrated in FIG. 5, if the decrease in thecalculation accuracy of the pre-correction SOC is detected, the fueleconomy control execution propriety determination process can becontinued by using the control SOC based on the second correction valueΔ2 for low accuracy state. Thus, the reduction in the chance to performthe fuel economy control can be suppressed. However, the calculation ofthe second correction value Δ2 for low accuracy state involves therefresh charging, as described above, which means that there is a casewhere the chance to perform the fuel economy control is lost due to thecalculation of the second correction value Δ2 for low accuracy state.

With respect to this, according to the process illustrated in FIG. 5,even if the decrease in the calculation accuracy of the pre-correctionSOC is detected, the second correction value Δ2 for low accuracy stateis not calculated to continue the fuel economy control executionpropriety determination process using the control SOC based on theaccuracy reservation margin M, if the control SOC at the time of thedetection of the decrease in the calculation accuracy is greater thanthe predetermined value Th1. Thus, the loss of the chance to perform thefuel economy control due to the calculation of the second correctionvalue Δ2 for low accuracy state can be suppressed. Further, the controlSOC based on the accuracy reservation margin M is used as long as thecontrol SOC at the time of the detection of the decrease in thecalculation accuracy is greater than the predetermined value Th1, whichcan ensures the reservation of the battery 60 when the SOC is thebattery 60 is low. Further, the control SOC based on the accuracyreservation margin M is calculated such that it is smaller than thecontrol SOC for high accuracy state, and thus the fuel economy controlin case of using the control SOC based on the accuracy reservationmargin M is prevented earlier than that in the case of using the controlSOC for high accuracy state. Thus, even if the control SOC based on theaccuracy reservation margin M is used, it is possible to increase aprobability that the fuel economy control is prevented before the actualSOC of the battery 60 becomes less than or equal to the controlpermission SOC.

It is noted that, according to the process illustrated in FIG. 5, if thedetermination result in step S506 is “YES”, and thus the process goes tostep S508, the process goes to step S514 if the control SOC based on theaccuracy reservation margin M becomes less than or equal to the controlpermission SOC (if the determination result in step S510 is “NO”).However, if the determination result in step S506 is “YES”, and thus theprocess goes to step S508, the process may go to step S514 if thecontrol SOC for high accuracy state becomes less than or equal to thepredetermined value Th1 (see time point t1 in FIG. 6).

FIG. 6 is a diagram illustrating an example of a change in time seriesof the control SOC based on the accuracy reservation margin M and theSOC for high accuracy state control. In FIG. 6, the control SOC based onthe accuracy reservation margin M is indicated by a solid line, and thecontrol SOC for high accuracy state is indicated by a dotted line.Further, the control permission SOC is indicated by “SOCt”.

In the example illustrated in FIG. 6, the decrease in the calculationaccuracy of the pre-correction SOC is detected at time point t0. At thattime, the control SOC (control SOC for high accuracy state) is greaterthan the predetermined value Th1, and thus the determination result instep S506 in FIG. 5 is affirmative. Thus, after that, the control SOCbased on the accuracy reservation margin M is calculated (step S508).After that, the control SOC based on the accuracy reservation margin Mbecomes less than or equal to the control permission SOC at time pointt2. In this case, the determination result in step S510 in FIG. 5 isnegative, and thus the calculation process of the second correctionvalue Δ2 for low accuracy state is performed (step S516). It is notedthat, as described above, instead of the time point t2 when the controlSOC based on the accuracy reservation margin M becomes less than orequal to the control permission SOC, the calculation process of thesecond correction value Δ2 for low accuracy state may be performed attime point t1 when the control SOC for high accuracy state becomes lessthan or equal to the predetermined value Th1.

FIG. 7 is a diagram illustrating an example of the change in time seriesof the control SOC in the high accuracy state and the low accuracystate. In FIG. 7, the control SOC is indicated by a solid line, theactual SOC is indicated by a dotted line, and an imaginary control SOCfor high accuracy state is indicated by a chain double-dashed line.Further, the control permission SOC is indicated by “SOCt”.

In the example illustrated in FIG. 7, the high accuracy state is formedbefore the time point t0. In this case, as illustrated in FIG. 7, thealienation between the actual SOC and the control SOC is small. Thealienation between the actual SOC and the control SOC basically becomesgreater according to a lapse of time. The decrease in the calculationaccuracy of the pre-correction SOC is detected at time point t0, and thecontrol SOC (control SOC for high accuracy state) at that time isgreater than the predetermined value Th1. For this reason, the controlSOC is changed at the time point t0 from the control SOC based on thefirst correction value Δ1 for high accuracy state to the control SOCbased on the accuracy reservation margin M. In other words, the controlSOC is changed to a value (i.e., the control SOC based on the accuracyreservation margin M) that is smaller than the control SOC for highaccuracy state (indicated by the chain double-dashed line) by theaccuracy reservation margin M. In the example illustrated in FIG. 7, thecontrol SOC based on the accuracy reservation margin M is greater thanthe control permission SOC afterward, and thus a state in which the fueleconomy control is executable is formed during this period.

FIG. 8 is a timing chart illustrating an example of a way of calculatingthe second correction value Δ2 for low accuracy state based on abehavior of a charge current I of the battery 60. The way illustrated inFIG. 8 may be used for the process in step S516 in FIG. 5, for example.FIG. 8 illustrates a course of charging the battery 60 to the chargelate state in which the charge current I of the battery 60 becomes lessthan a predetermined value Ith. The state of the battery 60 in thecharge late state corresponds to a substantially fully charged state(greater than or equal to 90%, for example) just before a fully chargedstate.

For example, in the case where the battery 60 is charged under a chargecondition of a constant low current and at a constant high voltage overa relatively long period, when the state of the battery 60 reaches thesubstantially fully charged state, the current value of the chargecurrent I suddenly decreases and the charge current I after timing t11becomes smaller than a predetermined current value Ith. After the timingt11, if the battery 60 is continuously charged under the same condition,a change rate of the charge current I becomes less than or equal to apredetermined decrease rate and a change rate of the SOC becomes lessthan or equal to a predetermined increase rate.

The battery 60 has such a charge characteristic that the SOC is equal toa constant coefficient S1 (95%, for example) at timing t12 that is aftera constant time Tth (two minutes, for example) has passed from thetiming t11 when the charge current I becomes smaller than thepredetermined current value Ith (3 A, for example).

Thus, the correction value calculation part 143 charges the battery 60under a charge condition of a constant low current and at a constanthigh voltage over a relatively long period, and calculates an offsetamount “a”, as the second correction value Δ2 for low accuracy state,between the coefficient S1 and the pre-correction SOC at the time when aconstant time Tth has passed since the charge current I becomes smallerthan the predetermined current value Ith. Thus, in the case of FIG. 8,the control SOC calculation part 144 calculates the control SOC(=coefficient S1) that is obtained by adding the offset amount “a” tothe pre-correction SOC at the timing t12.

According to the way of calculating the second correction value Δ2 forlow accuracy state illustrated in FIG. 8, it is possible to correct thepre-correction SOC with high accuracy even in the low accuracy state, bycorrecting the second correction value Δ2 for low accuracy state basedon the behavior of the charge current I in the charge late state.

All examples and conditional language recited herein are intended forpedagogical purposes to aid the reader in understanding the inventionand the concepts contributed by the inventor to furthering the art, andare to be construed as being without limitation to such specificallyrecited examples and conditions, nor does the organization of suchexamples in the specification relate to a showing of the superiority andinferiority of the invention. Although the embodiment(s) of the presentinventions have been described in detail, it should be understood thatthe various changes, substitutions, and alterations could be made heretowithout departing from the spirit and scope of the invention. Further,all or part of the components of the embodiments described above can becombined.

For example, according to the embodiments described above, at the timeof the detection of the decrease in the accuracy of the pre-correctionSOC, the control SOC is calculated by subtracting the accuracyreservation margin M from the control SOC for high accuracy state, andthe fuel economy control is permitted if the calculated control SOC isgreater than the control permission SOC. However, as an equivalentembodiment, at the time of the detection of the decrease in the accuracyof the pre-correction SOC, the control permission SOC may be correctedwhile continuously using the control SOC for high accuracy state. Inthis case, the control permission SOC is corrected by adding theaccuracy reservation margin M thereto. In this case, the fuel economycontrol may be permitted if the control SOC for high accuracy state isgreater than the corrected control permission SOC. Alternatively, thecontrol permission SOC may be corrected while calculating the controlSOC by subtracting the accuracy reservation margin M from the controlSOC for high accuracy state.

Further, according to the embodiments described above, the fuel economyprevention part 18 prevents or permits the charge control and the idlingstop control; however, only one of the charge control and the idlingstop control may be prevented. Further, the fuel economy prevention part18 may prevent only a part of the charge control that involves thedischarge.

Further, according to the embodiments described above, the control SOCcalculation part 144 calculates the control SOC in the high accuracystate by correcting the pre-correction SOC with the first correctionvalue Δ1 for high accuracy state; however, such a correction in the highaccuracy state may be omitted. For example, the battery capacitycalculation part 14 may calculate the pre-correction SOC as the controlSOC in the high accuracy state.

Further, according to the embodiments described above, the calculationof the second correction value Δ2 for low accuracy state involves therefresh charging; however, the refresh charging at that time may beperformed differently with respect to an ordinary refresh charging. Forexample, in the case of the ordinary refresh charging, a refreshcharging end condition may be met if the state of the battery 60 reachesa predetermined overcharged state (the overcharged state required forthe life preservation of the battery 60). On the other hand, in the caseof the refresh charging performed to calculate the second correctionvalue Δ2 for low accuracy state, the refresh charging end condition maybe met if the calculation of the second correction value Δ2 for lowaccuracy state is completed.

The present application is based on Japanese Priority Application No.2014-102753, filed on May 16, 2014, the entire contents of which arehereby incorporated by reference.

What is claimed is:
 1. A vehicle control apparatus comprising: a sensorthat obtains information related to a SOC (State Of Charge) of abattery; and a processing device that calculates the SOC based on theinformation from the sensor; determines whether the calculation value ofthe SOC is greater than a predetermined threshold; and permits anexecution of control that involves a discharge of the battery if thecalculation value of the SOC is greater than the predeterminedthreshold, wherein when the processing device detects a decrease inaccuracy of the calculation value of the SOC, the processing devicedetermines whether the calculation value of the SOC at a time ofdetection of the decrease is greater than a predetermined value that isgreater than the predetermined threshold, and if the calculation valueof the SOC at a time of detection of the decrease is greater than thepredetermined value, the processing device corrects at least one of thecalculation value of the SOC and the predetermined threshold to continuethe determination with the predetermined threshold, wherein at least oneof the calculation value of the SOC and the predetermined threshold iscorrected such that the execution of the control is permitted moredifficulty, within a range in which the execution of the control can bepermitted, with respect to a state before the detection of the decrease.2. The vehicle control apparatus of claim 1, wherein the processingdevice prevents the execution of the control if the calculation value ofthe SOC at a time of the detection of the decrease is less than or equalto the predetermined value.
 3. The vehicle control apparatus of claim 1,wherein if the calculation value of the SOC at a time of the detectionof the decrease is greater than the predetermined value, the processingdevice corrects the calculation value of the SOC by subtracting acorrection value therefrom.
 4. The vehicle control apparatus of claim 3,wherein the processing device prevents the execution of the control ifthe corrected calculation value of the SOC is less than or equal to thepredetermined value.
 5. The vehicle control apparatus of claim 2,wherein if the processing device prevents the execution of the control,the processing device calculates, during a period of the prevention, asecond correction value for the calculation value of the SOC.
 6. Thevehicle control apparatus of claim 5, wherein the processing deviceexecutes a charging process that causes the SOC of the battery toincrease to a maximum value during the period of the prevention, andcalculates the second correction value based on a change manner of acharge current of the battery in time series during the chargingprocess.
 7. The vehicle control apparatus of claim 6, wherein theprocessing device cancels the prevention after the calculation of thesecond correction value; corrects the calculation value of the SOC withthe second correction value; and performs the determination with thepredetermined threshold based on the calculation value of the SOCcalculated with the second correction value.
 8. The vehicle controlapparatus of claim 4, wherein if the processing device prevents theexecution of the control, the processing device calculates, during aperiod of the prevention, a second correction value for the calculationvalue of the SOC.
 9. The vehicle control apparatus of claim 8, whereinthe processing device executes a charging process that causes the SOC ofthe battery to increase to a maximum value during the period of theprevention, and calculates the second correction value based on a changemanner of a charge current of the battery in time series during thecharging process.
 10. The vehicle control apparatus of claim 9, whereinthe processing device cancels the prevention after the calculation ofthe second correction value; corrects the calculation value of the SOCwith the second correction value; and performs the determination withthe predetermined threshold based on the calculation value of the SOCcalculated with the second correction value.
 11. The vehicle controlapparatus of claim 1, wherein the processing device calculates a timeintegration value that is obtained by a time integration of absolutevalues of a charge current and a discharge current of the battery afteran ignition switch on event, and detects the decrease in accuracy of thecalculation value of the SOC if the time integration value exceeds asecond predetermined threshold.